Quoted monthly payment different from debited amount!!!

So i have been insured with Discovery for the past 4years or so, and in December 2017 i bought a new car and wanted that insured before taking delivery. I supp**** all the details as they have requested them including all the extras in the car. on the 15th of Dec there was a pro-rated amount debited on my account of R433 instead of the amount of R309.93 that we had agreed upon. on the 1st of Jan, my debit order goes through and to my surprise it is not the amount that we had agreed upon once again. According to my schedule my debit order should be R2255 and i was debited R2457. i have queried this with the service provider and i am told that it is because of the "extras" actually no one is telling me the real reason. i shopped around and when they quoted me the R2255 i accepted the quote but now they go and debit a different amount, this is ********* business practice.